Tesla shares fell on Monday after the electric-car maker’s chief executive Elon Musk said he would form a new political party, escalating a feud with US President Donald Trump.

Musk has been able to play off Tesla's struggles for over a year now because the stock has been astonishingly resilient. Neither political gaffe nor falling deliveries has knocked Tesla off its upward trajectory, but Monday's selloff may be a sign of a changing sentiment.